There is nothing wrong with visual reference. As I was taught, you should always use a combination of both imagination and reference. You can't get something right unless you look at it. For example, if you draw a car, you might draw something inadequate because you are relying too much on imagination. Always use photos to guide you. Its great to do things from a visual prospective but art books, and photo will bring your best ability out. I have ton of art books I use when I work on specific things. Use a combination of both. But if you really want to know what something looks like, go to the source.